The identification of thrombopoietin (TPO) has allowed the generation of megakaryocytes (MK) and platelets in ex vivo cultures. TPO and various cytokines have been shown to act in synergism for optimal MK viability and yield (Sigurjonsson OE, et al., J Hematother Stem Cell Res. 11:389-400, 2002; Williams J L, et al., Blood 91:4118-4126, 1998; Su R J, et al., Bone Marrow Transplant 27:1075-1080, 2001; and Kie J H, et al., Stem Cells 20:73-79, 2002). It has recently been reported that early and late variations of cytokine concentrations could promote the in vitro TPO-dependent generation of MKs from cord blood (CB) CD34-enriched cells (Proulx C, et al., J Hematother Stem Cell Res. 12:179-188, 2003). It is expected that other biochemical and/or biophysical factors could further enhance MK yield. Whole body hyperthermia in combination with chemo- or radiotherapy has been used for several years in the treatment of cancers. Animal and clinical data showed that transient body hyperthermia had several beneficial effects including more efficient bone marrow engraftment and protection against therapy-induced thrombocytopenia (Robins H I, et al. Cancer Res. 48:6587-6592, 1988; Robins H I, et al., J Clin Oncol. 11:1787-1794, 1993; Woods J P, et al., Can J Vet Res. 60:75-78, 1996; Robins H I, et al., J Clin Oncol. 15:158-164, 1997; Katschinski D M, et al., Cancer Lett. 115:195-199, 1997; and Katschinski D M, et al., Cytokine Growth Factor Rev. 10:93-97, 1999). These effects have been associated with rapid (60 minutes) increases of several cytokines in the plasma and bone marrow of hyperthermia-treated patients (Robins H I, et al., Cancer Lett. 97:195-201, 1995). Although these cytokines could have stimulatory effects, one cannot rule out a direct possible effect of hyperthermia on stem/progenitor cells.
It would be highly desirable to be provided with a new method for culturing MKs allowing to obtain better yield of cells than existing methods, thus further allowing a better platelet production than existing culture methods.